The present disclosure relates generally to the provision of power to an implanted medical device, and more particularly, to the provision of power to an auditory prosthesis.
Many implantable medical devices, such as auditory prostheses, are active implantable medical devices (AIMDs) which consume power. Such devices require power to be transferred from an external unit to an implanted unit. More recently, this transfer of power is generally performed transcutaneously since percutaneous leads may cause discomfort to and may be a potential source of infection.
The electronics in an auditory prosthesis typically consumes a small portion of the total electrical power consumed by the implantable unit of the prosthesis. The auditory prosthesis' components which are involved in sound amplification and generation consume the largest proportion of the implant's available power. Their power characteristic is generally dependent on the instantaneous sound intensity that is required during the implant's operation.
The radio-frequency (RF) signal sent to the implanted unit transfers energy that is used to power the implanted unit. Intermittencies can occur in the implanted unit's operation if insufficient power is transmitted to the implanted unit. On the other hand, excessive power can be consumed in the implanted unit if the power-determining parameters are too high. The intermittencies are the result of temporal modulations in the implanted unit's unregulated voltage, which technically represent an imbalance between power supplied to the implant and actual load demand.
The power in the RF signal is adjusted to avoid underpowering the implanted unit, i.e., to try to maintain a sufficient energy margin in the implant's tank capacitance and regulator. The power in the RF signal also is adjusted to avoid transients that overpower the implanted unit, i.e., to avoid circumstances in which the implanted unit's over-voltage protection circuits are in conduction.
A measurement of the implant's unregulated voltage and current, in some cases, is telemetered back periodically to the external speech processor (SP) to assist in the power level adjustment of the RF (carrier amplitude at resonance).